1. Field of the Invention
The present invention relates to a method for dicing a sapphire wafer for light-emitting devices such as light emitting diodes (LED) and laser diodes, which emit visible short-wave rays in the blue region of the optical spectrum. The invention further relates to a manufacturing method for gallium nitride compound semiconductor that utilizes a sapphire substrate wherein the above dicing method is utilized.
2. Description of the Related Art
A sapphire (Al.sub.2 O.sub.3) has been used as an insulative substrate for epitaxially growing gallium nitride (GaN) compound layers thereon.
A wafer of sapphire having semicondutor layers thereon is diced into chips by rotating a blade laminated with synthetic diamonds at high speed.
Since sapphire is harder than silicon, gallium arsenide, and so forth, dicing the sapphire wafer requires a blade with a wider width to rotate at higher speed and higher torque. Accordingly, the sapphire wafer diced by that blade produces chips with cracked edges (called chipping), dropping electrodes, and so forth. Consequently, many defective chips are produced by the conventional sawing method for dicing sapphire wafer.
In order to solve the chipping problem, several means have been proposed. Kotaki et al. discloses in Japanese Patent Application with Laid-Open No. 291147/1990 (2-291147) a dicing method of cutting a sapphire wafer, whose main surface is "a" {1120}, along a boundary crossing an axis "c" (0001) at 55 degrees or lower. Iwasa et al. discloses in Japanese Application with Laid Open No. 315646/1993 (5-315646) a method of cutting a sapphire wafer by cutting a groove deeper than the thickness of a GaN compound semiconductor layer on the sapphire wafer by a dicer, applying a scribing line by a scriber, and breaking the sapphire wafer into chip shaped dice using a load provided by a roller.
However, utilizing surface "a" {1120} of the sapphire wafer without defective chips has been difficult despite the proposed methods by Kotaki et al. and Iwasa et al. Extensive chipping is inevitable by the method of Kotaki et al., when the sapphire wafer is diced crossing an axis "m" (1010), which is a perpendicular in direction to the axis "c" (0001). Iwasa et al, inevitably uses the sapphire wafer whose main surface is "c" {0001}, because breaking the sapphire wafer to the direction of the axis "m" (1010) has been impossible by the grooving/scribing/rolling method of Iwasa et al.